FISHES. ■ 363 



the external they are more longitudinal, and their union is so very 

 slight that a solution of continuity, which has all the appearance of a 

 ventricle, is formed pretty frequently hctween them, but which is 

 shut in every part, and is. not even inside lined by a membrane*. 



The most vigorous of the fibres are in the bulb (y) of the branchial 

 artery, the greater part having a circular arrangement ; the name of 

 this part is derived from its form ; its communication Avith the ven- 

 tricle is supplied sometimes with two, sometimes with tliree membra- 

 nous valves ; but, frequently, in its interior, particularly in the 

 cartilaginous fishes, there are other ranges of small valves, and some- 

 times even these valves are fleshy. 



The prolongation of this bulb proceeds from the pericardium, and 

 becomes the branchial artery («), which is supported before as it pro- 

 ceeds beneath the azygos chain of small bones which unites the 

 branchial arches. 



The branchial artery is divided more or less immediately, but in 

 such a way as to give a branch to each brancliia. 



This branch (Q proceeds in a furrow which is excavated along the 

 convexity of each branchial arch, and more externally than the vein 

 which follows it in the same way but in a different direction. 



To this arch are attached a large number of parallel leaflets, 

 usually terminated in a forked point, and sometimes very deeply 

 divided ; the great branch whicli goes in the furrow of the arch gives 

 off a branch (^n) to each of the leaflets, and this branch after having 

 been twice bifurcated supplies an infinite number of small branchlets, 

 which creep across on each surface of the leaflet, and terminate by 

 being converted into minute veins ; these small veins on each side are 

 lost in a branchial vein (9) which jn-oceeds along the internal border 

 of the lateral lobe of the leaflet, and the two veins fall into the trunk 

 and great vein of the gill (a.) which is carried in the same furrow of 

 the artery, but more deeply, and which proceeds, besides, in a contrary 

 direction, that is to say, that the branchial artery coming from the 

 heart and from the ventral side, diminishes in proportion as it ascends 

 towards the back, and also that it furnishes small arteries, whilst the 

 branchial vein, on the contrary, receiving by the small veins and 

 other veins of the leaflets, the blood of these little arteries, increases 

 in proportion as it is carried towards the back. 



The rays have only two veins for each branchia whicli are not 

 xmited until after they pass out. 



The branchial veins, on leaving the dorsal side of the branchiae 

 (^ ix) assume the tissue and functions of arteries. The anteriors 

 had already sent, before leaving the branchia, several branches to 

 several parts of the head, and it is to be remarked, that the heart and 

 many places under the chest, receive their blood from a brancliial 

 vein by a ray which it sends to them near its origin, and, conse- 

 quently, long before its departure from the branchia. Still it is 



* M. DolliHger has described it in the cyprins. I have seen it very plainly in the 

 great svrord fish. M. Rathke thinks, and in my opinion Tvith some reason, that it 

 is produced by the commencement of decomposition. 



